It is known that perfluorinated organic compounds having functional moieties are useful intermediates for manufacturing a variety of valuable chemical compounds, such as perfluoromonomers (e.g. perfluorovinylethers) and fluorosurfactants.
A convenient approach for the synthesis of functional perfluorinated compounds involves fluorination of hydrogen-containing alcohols, the hydroxyl moiety being possibly derivatized to yield the target functional moiety. However, hydrocarbons containing functional hydroxyl moieties are generally unstable under conditions of traditional fluorination processes, typically comprising a first step carried out at low temperature and high dilution, followed by a further step involving high temperatures and high concentrations of fluorine, as required in order to reach satisfactory yields of the perfluorinated compound. Under these conditions, it is generally known that compounds having hydroxyl groups decompose, with simultaneous release of HF and COF2, and subsequent formation of corresponding non-functional perfluorocompound having one less carbon atom than the starting hydroxyl-containing compound.
In order to overcome this problem, EP 1164122 A (ASAHI GLASS CO LTD) 19 Dec. 2001 discloses a process for producing fluorinated compounds wherein a primary hydrogenated alcohol is first converted into the corresponding ester, generally a partially fluorinated ester, by reaction with an acyl fluoride, preferably a (per)fluorinated acyl fluoride, and then subjected to fluorination in liquid phase. The so-obtained perfluorinated ester can be then thermally cleaved or decomposed with suitable agents, to obtain a perfluorinated acyl fluoride corresponding to the starting hydrogenated alcohol.
Similarly, US 2003/0216595 (ASAHI GLASS CO LTD) 20 Nov. 2003 discloses a process for producing a fluorinated ester, wherein a primary or a secondary hydrogenated alcohol is converted into the corresponding ester by reaction with a (per)fluorinated acyl fluoride and then subjected to fluorination in liquid phase. The so-obtained perfluorinated ester can be thermally cleaved or decomposed with suitable agents, to obtain a perfluorinated acyl fluoride or ketone corresponding to the starting hydrogenated alcohol.
Fluorination of hydrogenated esters with molecular fluorine to obtain the corresponding perfluorinated compounds has been also previously disclosed. For instance, U.S. Pat. No. 5,093,432 (EXFLUOR RESEARCH CORPORATION) 3 Mar. 1992 discloses a process for the liquid phase fluorination of hydrogenated esters with fluorine in a perhalogenated liquid medium. The process is carried out under high diluted conditions. The use of trichloroethylene is mentioned as a cosolvent to improve the solubility of the hydrogenated starting material in the perhalogenated liquid medium.
However, the above described processes have the drawback that, in order to prevent decomposition of the reagents due to the reaction exothermicity, it may be necessary to operate under diluted conditions both of fluorine and of the hydrogen-containing starting material. Furthermore, to obtain a fully fluorinated product, a large excess of fluorine over the stoichiometrically required quantity, is needed. These conditions might negatively affect the reaction rate, yielding low productivity of the overall process.
Electrochemical fluorination of hydrogen-containing alcohols protected under the form of esters has also been disclosed. In particular, U.S. Pat. No. 3,900,372 (PHILLIPS PETROLEUM) 19 Aug. 1975 discloses a process for the production of perfluorinated organic compounds from hydrogen-containing alcohols. The process comprises protection of the hydroxyl moieties of the hydrogen-containing alcohol by reaction with a perfluorinated acyl fluoride, e.g. trifluoromethyl acyl fluoride, to yield the corresponding hydrogen-containing ester. Said ester is then subjected to an electrochemical fluorination step, and the resulting perfluorinated counterpart, still possessing the ester moiety, is subsequently cleaved by the action of fluoride ions to yield the corresponding perfluorinated acyl fluoride.
Nevertheless, electrochemical fluorination is a burdensome and energy-consuming procedure, which is generally less economically and industrially acceptable than fluorination with elemental fluorine, particularly when a single compound has to be obtained. Furthermore, yields in electrochemical fluorination are known to be mostly moderate or even poor, especially if high molecular weight compounds have to be fluorinated.
US 20060074260 A (KANEKO, Y. ET AL.) 6 Apr. 2006 discloses carrying out the fluorination process of a “substrate that cannot undergo a fluorination reaction independently” in the presence of a “substrate that rapidly undergoes a fluorination reaction independently”. The “substrate that rapidly undergoes a fluorination reaction independently” is defined as a compound having at least one (but preferably more than one) site at which reaction with fluorine can proceed. Notable examples of said substrates include linear, branched or cyclic hydrocarbon compounds having 5 to 30 carbon atoms, which may contain a fluorine atom, an oxygen atom, or/and an unsaturated bond, provided at least one unsaturated bond or at least on C—H bond are present. The examples however show that the addition of hexane as a “substrate that rapidly undergoes a fluorination reaction independently” was not sufficient to promote the complete fluorination of the starting ester compound and that the addition of a second substrate, namely hexafluorobenzene, was required to obtain a fully fluorinated product. Additionally, the yield of the fully fluorinated product was only 35%.
There is thus still a need in the art for a process for producing perfluorinated compounds having a functional moiety from hydrogen-containing alcohols comprising a fluorination step that may be carried out under mild conditions and providing high yields.